|  | 2.4 | The Spanning-Tree Protocol
| 2.4.1 | Overview of the spanning-tree protocol
The main function of the Spanning-Tree Protocol is to allow duplicate switched/bridged paths without incurring the latency effects of loops in the network. Bridges and switches make their forwarding decisions for unicast frames based on the destination MAC address in the frame. If the MAC address is unknown, the device floods the frame out all ports in an attempt to reach the desired destination. It also does this for all broadcast frames. The Spanning-Tree Algorithm, implemented by the Spanning-Tree Protocol, prevents loops by calculating a stable spanning-tree network topology. When creating fault-tolerant networks, a loop-free path must exist between all Ethernet nodes in the network. The Spanning-Tree Algorithm is used to calculate a loop-free path. Spanning-tree frames, called bridge protocol data units (BPDUs), are sent and received by all switches in the network at regular intervals and are used to determine the spanning-tree topology. A switch uses Spanning-Tree Protocol on all Ethernet and Fast Ethernet based VLANs. Spanning-Tree Protocol detects and breaks loops by placing some connections in a standby mode, which are activated in the event of an active connection failure. A separate instance of Spanning-Tree Protocol runs within each configured VLAN, ensuring Ethernet topologies that conform to industry standards throughout the network.
| Presentation (Microsoft® PowerPoint, 563kB)
| Spanning Tree Protocol
| Web Links
| Configuring Spanning Tree